Method for removal of radioactive contaminants



Patented Dec. 4, 1951 METHOD FOR REMOVAL OF RADIOACTIVE CONTAMINANTS Jack De Ment, Portland, reg., assig'nor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application April 2, 1947,

Serial No. 738,916

3 Claims.

The present invention relates to a method for the substantial lessening and mitigation of radioactively contaminated and polluted objects and areas.

This application is a continuation-in-part of my co-pending applications under title: Methods and Means for Reducing Radioactive Contamination, Serial Number 727,275, filed February 7, 1947, and, Method and Means for Lessening Radioactive Pollution, Serial Number 732,125, filed March 3, 1947, and, Radioactive Soap Compositions, Serial Number 725,970,

filed February 1, 1947 now abandoned.

This invention is also substantially related to the inventions disclosed in my co-pending applications under title: Methods and Means for Producing Radioactive and Isotopic Smoke, Serial Number 722,070, filed January 14, 1947 now abandoned; Method and Means for Producing Radioactive and Isotopic Aerosols, Serial Number 727,477, filed February 10, 1947; Radioactive Toxic Chemical Warfare Agents, Serial Number 729,875, filed February 20, 1947; Radioactive Toxic Incendiary Composition, Serial Number 732,919, filed March 6, 1947 now abandoned; and, "Radioactive and Radioactive Toxic Ammunition, Serial Number 735,144, filed March 17, 1947 now abandoned.

It is among the objects of this invention to mitigate, subsequent to the employment of atomic weapons, the danger of radioactive pollution and poisoning objects and areas susceptible thereto.

It is an object of the present invention to provide a method whereby military or naval or civilian installations may be rendered radioactively less dangerous by the removal of radioactive contaminants therefrom.

It is among the objects of this invention to supply improvements in the radioactive decontamination art effective to a plurality of radioactive substances, both soluble and insoluble in character, as well as inert and radioactive gases and vapors, that may give rise to the contamination condition.

It is an object of this invention to provide a method for the mitigation of the danger of radioactive poison whereby the mitigation and removal method may be carried out afar from the site of contamination and pollution. Thus, after cess of personnel to the ship is prevented. By

means of the present invention, mitigation of such danger" may be carried on by remote control, from aircraft and radio controlled sea-craft and land-craft.

In the present invention a silicon compound or derivative of a hydrolysable or soluble character is relied upon for the mitigation of radioactive contamination. There are a number of forms which this invention can take, and infra are disclosed several preferred illustrations of the method, but these are not to be taken as limiting, for wide departures may be made without violating the spirit nor the scope of this invention.

After use of an atomic weapon like an atomic bomb there is left a plurality of dangerous radioactive products, frequently solid particles of a soluble or insoluble kind, and it is a problem of the greatest magnitude to safely and effectively remove such after-products, by-products and atomic debris. Briefly, this invention is directed to a method whereby substances may be em ployed which react with the soluble radioactive compounds to form substantially insoluble derivatives thereof, which also carry by adsorption, absorption and other mechanical means such insoluble products as may be unreactive, and which possess large adsorptive powers for radioactive gases and vapors, whether these be inert' or reactive.

As a general class of materials and procedures fulfilling the requirements for radioactive pollution mitigation this invention relies broadly upon certain reactive compounds of silicon, which upon reaction and use undergo a complex series of chemical and physical reactions and processes, many of which are of utility in achieving the hereinbefore set forth objects.

Example 1.-In one embodiment of this invention a solution of a soluble silicate may be applied to the said target or object or area. A soluble silicate, like a derivative of the alkali metal group of elements, e. g., sodium or potassium, hydrolyses upon reaction with dilute acid to give silicic acid in a number of forms, first produced in a colloidally suspended state, later changing to a gelatinous or jellified mass; furthermore, a soluble silicate reacts with many soluble salts of heavy metals, which may comprise part of the radioactive contaminant, to produce insoluble metallic silicates which are absorbed, mechanically mixed, dispersed, and otherwise carried within the body of silicic acid and its subsequent gewater; finally, the silicic acids possess excellent I adsorbing properties for gases and vapors of many substances, including the inert radioactive gases which are coincident to use of atomic weapons or the disintegration of by-products and after-products.

It is thus evident that when a solution of a soluble silicate is applied to a radioactively contaminated object that all of the processes and reactions proceed as given supra, particularly subsequent to the use of a reactant which enables the formation of silicic acids and the like.

Therefore, it is the preference in employment of this form of the present invention to utilize in sequence a soluble silicate, a material like hydrochloric acid in dilute solution, and such other media as may be desired and deemed necessary to enable reaction, water for example.

As the soluble silicate the compound known as sodium silicate in the form of water glass, diluted with water, is preferable and usable. The

, state, and after radioactive pollution, the rending of the said silicon compound so as to effect processes and reactions disclosed under Example 1 Thus a solid or substantially solid, e. g., tacky liquid coating or adhesive particles, or, coating of thick semi-dried gel or the like, of a silicon compound of the character set out in Example 1 may be initially applied to the target before attack by atomic weapons. As examples of such usable materials there are the dry sodium silicates, or soluble glasses, compositions commonly available including: NazSiOa, NaaSizO'z and Na2Si3O7. These substances all have varying amounts of water present, and the physical characteristics may be governed by the water content. The first-named compound has approxiwater glass or sodium silicate compositions of commerce are of varying composition with respect to the ratio between sodium and silicon dioxide, as well as of various densities. One common form can be employed, and this is the 40 per cent NazSiaOv, water glass, of commerce. Other concentrations may also be used, and this invention is operable when the 40 per cent composition is diluted several times with water. The greater the ratio of NazO to SiO-z the greater the alkalinityand the more tacky the solution.

Solutions of soluble silicate, like the sodium silicate set out supra, are readily decomposed by dilute or strong acids with the occurrence of the processes described hereinbefore. In water such compounds hydrolyze to give strongly alkaline.

solutions, since they are the salt of a strong base and a weak acid.

The present invention as illustrated by the present example therefore comprises the application to a radioactively contaminated object of a solution of soluble silicate, like sodium silicate, and the subsequent application of dilute acid, say hydrochloric acid ranging in concentration from 5 per cent to 20 or 30 per cent, as desired, and as governed by the nature of the polluted object. The application of these materials, by method and means herein set forth, as well as disclosed in the co-pending applications referred of a silicon compound in a substantially solid mately five water molecules present in its structure. In general, the materials are obtained as colorless or white or greyish-white crystal-dike lumps and particles. It is the preference, for wide application, to employ fine mesh powderforms of these compounds, say 0150 or mesh fineness, though this is optional. These silicates are diflicultly soluble or almost soluble in cold water, and therefore they are of utility when a target or object must be treated and maintained in such a condition for a long period of time. They are best brought into solution by heating with hot water or water under pressure, and are less readily soluble in much water than in little water, and the anhydrous forms dissolve with more difficulty than the hydrated forms; also, the silicates containing more sodium' dissolve more readily.

Such compounds may be applied in viscous liquid form to the surface of an object, the said object thereupon heated so as to drive out water effective to leave a coating comprised of a more or less solid form of the silicate, or, the particles of the silicate may be mechanically dispersed over the surface of a target in anticipation of atomic weapon usage, or, the particles may be mechanically mixed with the strippable composition of the nature disclosed in my co-pending application entitled Method and Means for Lessening Radioactive Pollution, Serial Number 732,125, filed March 3, 1947, or, the solid and semi-solid silicate mixtures may be applied in any fashion as dictated by the conditions, the treatment procedure not being novel and carryable 0n according to knowledge well known in the art.

In rending the silicate so as to produce the processes and reactions and changes of composition and physical characteristics described under Example 1 subsequent to contamination, hot water under pressure, say from a steam gun, may be used, then acid as given in Example 1, or both at once, and finally water in amount and number of repititious applications as may be necessary to bring radiation level down to substantially tolerance values. If the silicate is employed in connection with the method and means disclosed in the above-named co-pending application, the acid or similar reactant will form a part of the method and means of that invention in which a stripping composition is employed to remove a strippable composition.

I claim:

1. The method of removing radioactive contaminants from a surface comprising the steps of applying a sodium silicate to the surface, forming silicic acid by treating the sodium silicate with a dilute solution of a strong mineral acid and removing the reaction products and unannals 6 reacted materials together with radioactive con- UNITED STATES PATENTS taminants carried therewith. N ber Na 2. The process of claim 1 wherein the acid is 23 wuth f g hydrochloric acid having a concentration of from 1,111,445 Dunton 1914 5 to 30% 5 2,020,228 Ashton Nov, 5, 1935 3. The process of claim 1 wherein the sodium 2 029 992 Ems Feb 4 1936 silicate is Na2Si3O7.

JACK DE MENT' 2,377,062 Adams May 29, 1945 OTHER REFERENCES REFERENCES CITED 10 Gilman: Inorganic Reactions, published by The following references are of record in the Eclectic Publishers (1929)- P file of this patent: Sollman: A Manual of Pharmacology," sixth edition (1942), pages 60-63. 

1. THE METHOD OF REMOVING RADIOACTIVE CONTAMINANTS FROM A SURFACE COMPRISING THE STEPS OF APPLYING A SODIUM SILICATE TO THE SURFACE, FORMING SILICIC ACID BY TREATING THE SODIUM SILICATE WITH AD DILUTE SOLUTION OF A STRONG MINERAL ACID AND REMOVING THE REACTION PRODUCTS AND UNREACTED MATERIALS TOGETHER WITH RADIOACTIVE CONTAMINANTS CARRIED THEREWITH. 